Mempool

Endpoints to obtain Mempool information

Get mempool transaction fee priorities

get

Returns estimated fee priorities (in micro-STX) for all transactions that are currently in the mempool. Also returns priorities separated by transaction type.

Responses

200

Default Response

application/json

4XX

Default Response

application/json

get/extended/v2/mempool/fees

GET /extended/v2/mempool/fees HTTP/1.1
Host: api.hiro.so/
Accept: */*

{
  "all": {
    "no_priority": 1,
    "low_priority": 1,
    "medium_priority": 1,
    "high_priority": 1
  },
  "token_transfer": {
    "no_priority": 1,
    "low_priority": 1,
    "medium_priority": 1,
    "high_priority": 1
  },
  "contract_call": {
    "no_priority": 1,
    "low_priority": 1,
    "medium_priority": 1,
    "high_priority": 1
  },
  "smart_contract": {
    "no_priority": 1,
    "low_priority": 1,
    "medium_priority": 1,
    "high_priority": 1
  }
}

Get mempool summary

get

Retrieves a summary of the transactions currently pending in the mempool: how many there are, and the fee, size, and receipt percentiles across them, both overall and broken down by transaction type. Percentiles are discrete: each is a value some pending transaction actually has, not an interpolation between two of them.

Responses

200

A summary of the transactions currently pending in the mempool. Top-level metrics cover every pending transaction; by_type breaks the same metrics down by transaction type, so the top-level count always equals the sum of the per-type counts. Only the types a client can broadcast are reported: coinbase, tenure-change, and poison-microblock transactions are miner-internal or no longer produced, and are excluded throughout.

application/json

A summary of the transactions currently pending in the mempool. Top-level metrics cover every pending transaction; by_type breaks the same metrics down by transaction type, so the top-level count always equals the sum of the per-type counts. Only the types a client can broadcast are reported: coinbase, tenure-change, and poison-microblock transactions are miner-internal or no longer produced, and are excluded throughout.

countintegerRequired

Number of pending transactions in this bucket

Example: 1203

4XX

Default Response

application/json

get/extended/v3/mempool

GET /extended/v3/mempool HTTP/1.1
Host: api.hiro.so/
Accept: */*

{
  "count": 1203,
  "fee_rate": {
    "p25": "250",
    "p50": "250",
    "p75": "250",
    "p95": "250"
  },
  "tx_size": {
    "p25": 241,
    "p50": 241,
    "p75": 241,
    "p95": 241
  },
  "receipt_time": {
    "p25": 1789431980,
    "p50": 1789431980,
    "p75": 1789431980,
    "p95": 1789431980
  },
  "receipt_block_height": {
    "p25": 214500,
    "p50": 214500,
    "p75": 214500,
    "p95": 214500
  },
  "by_type": {
    "token_transfer": {
      "count": 1203,
      "fee_rate": {
        "p25": "250",
        "p50": "250",
        "p75": "250",
        "p95": "250"
      },
      "tx_size": {
        "p25": 241,
        "p50": 241,
        "p75": 241,
        "p95": 241
      },
      "receipt_time": {
        "p25": 1789431980,
        "p50": 1789431980,
        "p75": 1789431980,
        "p95": 1789431980
      },
      "receipt_block_height": {
        "p25": 214500,
        "p50": 214500,
        "p75": 214500,
        "p95": 214500
      }
    },
    "smart_contract": {
      "count": 1203,
      "fee_rate": {
        "p25": "250",
        "p50": "250",
        "p75": "250",
        "p95": "250"
      },
      "tx_size": {
        "p25": 241,
        "p50": 241,
        "p75": 241,
        "p95": 241
      },
      "receipt_time": {
        "p25": 1789431980,
        "p50": 1789431980,
        "p75": 1789431980,
        "p95": 1789431980
      },
      "receipt_block_height": {
        "p25": 214500,
        "p50": 214500,
        "p75": 214500,
        "p95": 214500
      }
    },
    "contract_call": {
      "count": 1203,
      "fee_rate": {
        "p25": "250",
        "p50": "250",
        "p75": "250",
        "p95": "250"
      },
      "tx_size": {
        "p25": 241,
        "p50": 241,
        "p75": 241,
        "p95": 241
      },
      "receipt_time": {
        "p25": 1789431980,
        "p50": 1789431980,
        "p75": 1789431980,
        "p95": 1789431980
      },
      "receipt_block_height": {
        "p25": 214500,
        "p50": 214500,
        "p75": 214500,
        "p95": 214500
      }
    }
  }
}

Get mempool transactions

get

Retrieves a list of recently broadcasted transactions

Query parameters

limitinteger · min: 1 · max: 50Optional

Number of results per page

Default: 20

cursorstringOptional

Cursor for paginating mempool transactions. Format: receipt_time:tx_id

Pattern: ^\d+:(0x)?[a-fA-F0-9]{64}$

Responses

200

Default Response

application/json

totalintegerRequiredExample: 1

limitinteger · min: 1 · max: 50Required

Number of results per page

Default: 20

4XX

Default Response

application/json

get/extended/v3/mempool/transactions

GET /extended/v3/mempool/transactions HTTP/1.1
Host: api.hiro.so/
Accept: */*

{
  "total": 1,
  "limit": 20,
  "cursor": {
    "next": "text",
    "previous": "text",
    "current": "text"
  },
  "results": [
    {
      "tx_id": "text",
      "sender": {
        "address": "text",
        "nonce": 1
      },
      "sponsor": {
        "address": "text",
        "nonce": 1
      },
      "fee_rate": "text",
      "receipt_time": 1,
      "receipt_time_iso": "2026-10-08T19:18:41.000Z",
      "receipt_block_height": 1,
      "status": "pending",
      "type": "token_transfer",
      "token_transfer": {
        "recipient": "text",
        "amount": "text",
        "memo": {
          "hex": "text",
          "repr": "text"
        }
      }
    }
  ]
}